Aussant was elected to the National Assembly of Quebec in the 2008 general election, defeating his Liberal opponent by only 141 votes. This was the second closest result in the province. The Liberals won a majority government across the province under Jean Charest's leadership, and the Parti Québécois formed the official opposition. Aussant was appointed as his party's critic for financial institutions and international commerce and became an opposition representative on the legislative committee on public finances. He questioned the Charest government's appointment of Michael Sabia as head of the Caisse de dépôt et placement du Québec in May 2009, arguing that Sabia had tried to move BCE Inc.'s upper management and operations from Montreal to Toronto and could not be trusted to represent Quebec's interests. The following year, Aussant accused Sabia of having cost Quebecers $6 billion as the result of a poor risk management strategy. When Quebec investment advisorEarl Jones was accused of stealing money from his clients in 2009, Aussant called for new legislation requiring financial advisors to register with the province's financial markets authority. He also called for the Charest government to create a parliamentary commission on economic crime. In 2010, Aussant argued that Quebec could save about $840 million by removing the Canada Revenue Agency from tax collection in Quebec. He later criticized a proposed merger of the London Stock Exchange with the TMX Group, arguing that it would be "a further loss of ground for Quebec." Aussant was a member of the PQ's hardline indépendantiste wing. Before leaving the party, he founded a video touring series with three other PQ MNAs to promote the benefits of an independent Quebec, called the ABCD.
Independent
On June 7, 2011, Aussant followed caucus-mates Louise Beaudoin, Pierre Curzi, and Lisette Lapointe in resigning from the Parti Québécois caucus. Unlike the first three legislators who criticized PQ leader Pauline Marois for supporting a bill that endorsed a controversial agreement between Quebec City and Quebecor Inc. on the construction of a new arena, Aussant criticized Marois for downplaying Quebec sovereignty and called on her to resign as party leader. Aussant sat in the legislature as an independent. During this period, he submitted various bills to the National Assembly, including Bill 596 -Act to modernize Quebec’s democratic institutions- covering topics such as the implementation of a proportional electoral system, fixed-date elections, the end of private funding for political parties and the possibility for electors to bring popular initiatives to the National Assembly if the support of at least 5% of the electors is gathered. He dismissed suggestions that he could join a new political movement led by former PQ minister François Legault, stating that he and Legault were on opposite sides of the sovereignty issue and describing Legault's movement as "populism of the worst kind."
Option nationale
Following his departure from the PQ, Aussant created his own political party, Option nationale, which officially became registered on October 31, 2011. The party proposed to be more committed to Quebec sovereignty than the Parti Québécois, and would seek an electoral mandate for full-fledged autonomy, before a referendum to adopt the constitution of Quebec as an sovereign nation-state. No Option Nationale candidates were elected in the ensuing election; Aussant lost his seat to a Coalition Avenir Québec candidate. On June 19, 2013, Aussant left his role as leader of the party. He stated "family and personal matters" as the official reason. In August of the same year, he announced that he would be leaving Quebec to work once again with Morgan Stanley Capital International in Britain. He noted that he had not received job offers from Quebec employers and speculated that his involvement in the Quebec separatist movement may have been the reason.
Return to the Parti Québécois
Aussant rejoined the Parti Québécois, and ran as its candidate in the 2018 election in the riding of Pointe-aux-Trembles. However, he was defeated.
